This invention relates to a rewritable optical recording medium that can optically record, reproduce and erase information by light and heat, a method for recording information on the optical recording medium and reproducing the recorded information and a method for erasing the recorded information. Furthermore, the present invention relates to an article utilizing the properties of the optical recording medium.
Recently, researches and developments have been vigorously made on information recording media capable of recording information at desired parts at a high density and a high speed, and optical recording media capable of recording and reproducing information by irradiation of laser beam spot and erasing the recorded information and rewriting new information by the laser beam have been so far proposed.
The conventional optical recording media can be classified into various types such as a pit-forming type, a bubble or uneven surface-forming type, a photomagnetic type, a phase change type, etc. on the basis of what physical change is brought to the medium when heated by a laser beam spot, 1.5 .mu.m in diameter, as disclosed in Nikkei Electronics January 4 issue (1982), page 86 et seq. under the title "Optical disk memory that has been just used in image files".
Among these types, only optical recording media of phase change type are rewritable. So far proposed optical recording media of phase change type are those having a thin film comprising a composition containing a chalcogenide based material or a lower oxide (Japanese Patent Publication No. 47-26897).
The optical recording media of phase change type include those based on a phase change between the amorphous state and the crystalline state or between one crystalline state and another crystalline state. Chalcognide-based substances mainly belong to the phase change type between the amorphous state and the crystalline state and include those disclosed in the Japanese Patent Publication No. 47-26897 and tellurium compounds, etc. disclosed in Japanese Patent Application Kokai (Laid-open) No. 60-253034. Cu-Al-Ni alloy or In-Sb alloy disclosed in Japanese Patent Application Kokai (Laid-open) No. 60-46339 belong to the phase change type between the crystalline states. In these optical recording media, recording and erasing are carried out by reversibly changing the structural state from one to another or vice versa. In those media of phase change type between the amorphous state and the crystalline state, recording and erasing are carried out by using the amorphous state for a recording state and the crystalline state for an unrecording state.
One of the important requirements for an optical recording medium is higher speed recording and erasing.
Conventional, rewritable optical recording media of phase change type, including those of phase change type between the amorphous state and the crystalline state and those of phase change type between one crystalline state and another crystalline state have such a problem as low speed erasing.